Dave Airlie has a message on his blog about a 2D Linux driver he wrote for a Radeon X1300 card that he wishes to be open-source, but the code hasn't yet been reviewed by ATI.
I wrote a driver for my X1300 card for 2D using that info and a VBE modesetting tool that trapped all the IO accesses. The code mod to the radeon driver is about 600 lines of actual code. I submitted this to ATI for release due to the NDAs I have with them. It is now > 4 months since I did this and I've heard nothing back from ATI apart from the initial interface.